1. Field of the Invention
The present invention relates to materials used in a gland packing made from expansive graphite, the gland packing made from expansive graphite made from the materials and a producing method of gland packing made from expansive graphite, and more particularly, it relates to the materials used in a gland packing with producing facility in addition to sealing ability, heat resistance, chemical resistance and such properties and without causing electrolytic corrosion to a shaft and an apparatus casing, made from expansive graphite, the gland packing made from expansive graphite made from the materials and a producing method of gland packing made from expansive graphite.
In the specification, allowable tensile force means the product of a tensile strength of the materials, and the cross-sectional area of the materials in a case of the materials resulting in a fracture.
2. Description of the Related Art
As a packing which carries out a shaft sealing of fluid apparatus, there have been a gland packing made from expansive graphite hitherto. The gland packing made from expansive graphite is packed in a room which is formed in-between a shaft and an apparatus casing, i.e., the inside of staffing box, in order to prevent fluid from leaking out from in-between the shaft and the apparatus casing.
Expansive graphite surpasses in lubricating ability, heat resistance, chemical resistance and such properties, but on the other hand, it has defects that its tensile strength is weak and also is fragile. Thus, when constructing a sheet from expansive graphite and twist processing such sheet, there have been many circumstances wherein said sheet fractures due to a big tensile force reacted thereto. From such reasons, there have been a few circumstances wherein a gland packing made from expansive graphite is constructed from expansive graphite by itself, and it is usually produced in a form which is reinforced with other materials.
As for a gland packing made from expansive graphite which has a reinforced structure, the following has been suggested.
For example, a gland packing made from expansive graphite wherein: a laminated sheet is constructed by laminating a cotton threaded fabric sheet on one surface of expansive graphite sheet; a strip laminated sheet is formed by cutting such laminated sheet; braiding thread is constructed by a twist processing of such laminated sheet so that the strip laminated sheet covers a reinforcing wire and that the expansive graphite sheet positions on the outside; and after this, such braiding thread is braided into a gland packing made from expansive graphite, is suggested.
In this example, when twist processing the laminated sheet and braiding the braiding thread, tensile force reacts to the expansive graphite sheet. However, the expansive graphite sheet will not fracture because it is reinforced with the cotton threaded fabric sheet.
However, with the above mentioned prior art, there were some problems that follow.
That is, since tensile strength of cotton thread is not very high, in order for the cotton threaded fabric sheet to function sufficiently as a reinforcing material, it was necessary to have the sectional area of said sheet bigger. To hitherto correspond to this necessity, the width of cotton threaded fabric sheet was widened by winding the width of strip laminated sheet. However, it was difficult to gain braiding thread of good quality from the laminated sheet with such width. This was because the flexibility of the laminated sheet gets lower as the width of thereof becomes over 10 mm, causing a difficulty in a twist processing. Further, the braiding thread gained in such way was inferior in flexibility, causing a difficulty when braiding thereof.
Furthermore, the gland packing made from expansive graphite which was gained by braiding with this braiding thread is also inferior in flexibility. If such gland packing made from expansive graphite with low flexibility was packed in the stuffing box, it might not be possible to secure sufficient sealing ability, even when the gland was bound tightly.
Also, the expansive graphite positioned on the outside of the gland packing made from expansive graphite. From doing this, the expansive graphite was touching to the shaft and the apparatus casing. The expansive graphite is a conductive material, and the shaft and the apparatus casing are also constructed with conductive materials such as metals. Therefore, an electric potential difference is created between the expansive graphite and the shaft, and between the expansive graphite and the apparatus casing, thus, there might be a risk of generating a electrolytic corrosion.